The present invention relates generally to a diaphragm clutch mechanism, in particular for a motor vehicle, of the kind comprising a first substantially annular part comprising a cover, a second substantially annular part comprising a diaphragm spring, which has a peripheral part forming a cup spring and a central part divided into radial fingers, connecting means fixing the diaphragm spring to the cover for pivotal movement with respect thereto, and a third annular part comprising a pressure plate which is connected to the cover for rotation with the cover whilst at the same time being axially movable relative thereto, and on which the diaphragm spring bears by means of its peripheral cup spring part.
By means of its cover, a clutch mechanism of this kind can be attached to a reaction plate or flywheel, which is connected with a first shaft (usually a driving shaft) for rotation therewith with the interposition between this reaction plate and the pressure plate of a friction disc which is connected for rotation with a second shaft (usually a driven shaft). A clutch bearing is generally arranged around the driven shaft and is capable of acting on the radial fingers of the diaphragm spring in order to release the clutch, which is normally engaged. In this normal condition the pressure plate clamps the friction disc against the reaction plate under the action of the peripheral cup spring part.
The present invention relates more particularly to clutch mechanisms of this kind in which the connecting means fixing the diaphragm spring to the cover for pivoting movement comprise, on the one hand, flat, thin lugs which are integral with the cover, on which bear on the cover, and which pass, by means of an axial part, through openings provided in the diaphragm spring in the region of the base of the radial fingers spring, and which define an axial retaining bend on the other side of this diaphragm, and, on the other hand, a pivot ring which is interposed between the axial retaining bend and the peripheral part of the diaphragm spring, and which is anchored between this axial retaining bend and a transverse shoulder of the axial part of the lugs, forming a flange on the axial part.
A clutch mechanism of this type is described in U.S. Patent Application Ser. No. 160,460 filed June 18, 1980.
In the construction described in this prior U.S. application, the shoulder of the axial part of each lug, on which shoulder the retaining ring bears axially for its anchorage, is in contact with both of the axial edges of the axial part of this lug and is equally distributed over both of these axial edges.
Although this arrangement can be satisfactory, it has the following disadvantages.
Firstly, circumferentially, the axial part of each lug necessarily has only a limited extension, with the result that the division, into two portions, of the transverse shoulder which this axial part possesses for the anchorage of the pivot ring accordingly reduces, circumferentially, the individual extension of each of these shoulder portions, or, in other words, leads to shoulder portions which each individually possess, circumferentially, a very reduced extension.
Now, the stamping-out of the initial blank leading to the formation of these lugs results in the presence of round-offs or hollows at each of the ends of the shoulder portions which the axial part of this lug possesses.
These round-offs or hollows inevitably encroach on the length of material available for the formation of this shoulder portion, with the result that the rectilinear part, which can therefore have this shoulder portion between its two end round-offs, is extremely reduced or even non-existent.
Consequently, the zone in which the pivot ring bears on this shoulder portion is poorly defined and is difficult to control.
Thus, the anchoring contact of the pivot ring with the shoulders of the axial lugs used to fix it to the cover may not be satisfactory, to the detriment of the working conditions of this pivot ring.
Moreover, difficulties appear when the various components required to build up the clutch mechanism are stacked together. These difficulties essentially involve the engagement of the diaphragm spring on the lugs intended for fixing it to the cover.
In fact, because the axial part of these lugs has, on each of its axial edges, a shoulder portion for the bearing of the retaining ring, the diaphragm, it it is not presented correctly (the tolerances in this respect being very low), can be stopped prematurely by one or other of the shoulder portions of one or other of these lugs, in particular in the case where the stacking is carried out by means of an automatic machine.
However, these difficulties also involve the pivot ring, albeit to a much less serious extent.
In fact, because of the narrowness of each of the shoulder portions of the axial part of the lugs on which it is to bear, the tolerances for engagement of this pivot ring on these lugs are also extremely low.
The present invention relates in general terms to an arrangement which makes it possible to avoid these disadvantages.